STAT4 Regulates the CD8+ Regulatory T Cell/T Follicular Helper Cell Axis and Promotes Atherogenesis in Insulin-Resistant Ldlr−/− Mice

Abstract

The metabolic syndrome and diabetic conditions support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. While the pro-inflammatory role of signal transducer and activator of transcription 4 (STAT4) in atherosclerosis and diet-induced insulin resistance (IR) was recently established, an impact of STAT4 on atherogenesis in conditions of IR is not known. Here we generated Stat4−/−Ldlr−/− mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC fed Stat4−/−Ldlr−/− mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr−/− controls. Interestingly, we detected a reduction in T follicular helper (Tfh) and plasma B cells, but a sharp elevation in CD8+ Tregs in spleens and aortas of Stat4−/−Ldlr−/− versus Ldlr−/− mice. Similarly, STAT4 deficiency supported CD8+ Treg differentiation in vitro. Stat4-deficient CD8+ Tregs suppressed Tfh and germinal center B cell development upon immunization with KLH indicating an important role for STAT4 in CD8+ Treg functions in vivo. Furthermore, adoptive transfer of Stat4−/−Ldlr−/− CD8+ Tregs vs Ldlr−/− CD8+ Tregs resulted in a significant reduction of plaque burden, suppression of Tfh and germinal center B cells in DDC fed Ldlr−/− recipients. STAT4 expression in macrophages also affected the Tfh/CD8+Treg axis, as conditioned media from Stat4−/−Ldlr−/− MΦs supported CD8+ Treg but not Tfh cell differentiation in TGFβ-dependent manner. These findings suggest a novel mechanism by which STAT4 supports atherosclerosis in IR Ldlr−/− mice via STAT4-dependent macrophage as well as cell-intrinsic suppression of CD8+ Treg generation and functions and maintenance of Tfh cell generation and accompanied humoral immune response.

Phase 1 double-blind randomized safety trial of the Janus kinase inhibitor tofacitinib in systemic lupus erythematosus

“…The mechanism of this finding of short-term tofacitinib exposure leading to improvements in arterial compliance and endothelial function remains speculative. Higher prevalence of the STAT4 risk allele has been associated with cardiovascular risk in SLE patients and atherosclerosis animal models 16,39 . In this study, HDL function (as measured by LCAT activity), arterial stiffness, and endothelium-dependent vasorelaxation improved in individuals on tofacitinib that were positive for STAT4 risk allele.…”

Insights Into the Molecular Mechanisms of T Follicular Helper-Mediated Immunity and Pathology

“…In autoimmune-prone mice, CD8 Tfr cells can suppress the expansion of Tfh cells as well as autoantibody production ( 190 ). Recent data indicate on the importance of the TF STAT4 for CD8 + Tfr development, maintenance, and function toward Tfh and plasma B cells ( 191 ). Moreover, CD8 Tfr cells expressing IL-2Rβ are also shown to inhibit CD8 T cell function in an IL-10-dependent manner ( 192 ).…”

TRAM-Related TLR4 Pathway Antagonized by IRAK-M Mediates the Expression of Adhesion/Coactivating Molecules on Low-Grade Inflammatory Monocytes

“…With particular relevance, enhanced CD8 T cell activation and reduced CD8 1 CD122 1 T regulatory cells are closely related to enhanced pathogenesis of atherosclerosis, both in animal models and human patients with coronary artery diseases (4143). Although monocytes have been implicated in the modulation of CD8 1 CD122 1 T regulatory cells, molecular mechanisms were not well understood (41,43). Given our observation that lowgrade inflammatory monocytes express elevated levels of CD11a and CD40, we then tested whether low-grade inflammatory monocytes may selectively reduce the CD8 1 CD122 1 T regulatory cell population in vitro.…”